A Varroa-mediated transmission cycle can cause two DWV virus types (normally only found in low levels in healthy hives) to establish in bee colonies: Type A (lethal) and type B (non lethal). In hives not treated for varroa which had a stable colony of bees, only type B virus was found. The tested colonies belonged to Ron Hoskins, who has not treated his bees for 19 years. By allowing natural selection, and in a known process called Superinfection Exclusion, it is suggested that the non lethal type B virus prevented the virulent lethal type A virus from establishing.

The MBA’s Gideon Mordecai, lead author of the research said

“It was great to see that through the process of natural selection, honey bees, Varroa and DWV were able to reach a stable state, with honey bee colonies able to survive without the use of a chemical Varroa treatment.”

It is likely that genetically resistant strains of bees and learned grooming behaviour are also an element in establishing a stable colony, but this new finding is an important part of understanding why colonies of beekeepers who do not treat their bees do not collapse, and how preventing natural selection can ultimately weaken bees.